The most common type of wind turbines have been designed for maximising power generation, for scale and levels of efficiency, and how they could constitute an alternative to fossil fuels. That has meant huge, expensive pieces of engineering that have had no place in urban areas or close to homes: they're too dangerous, too noisy.
There is huge potential for reducing energy demand and carbon emissions from the mass take-up of small wind turbines
Small-scale wind turbines have yet to become as common as solar panelling on residential homes, public buildings or business locations, mostly due to issues of performance, size and cost. In other words, it’s a design issue. There is huge potential — both commercially and in terms of the evolution of self-powering homes and businesses — for reducing energy demand and carbon emissions from the mass take-up of small wind turbines. In the UK, given the weather patterns, the combination of solar panels and wind turbines are a more practical, sustainable solution.
At Cranfield University, the testing of a new generation design is underway. This is based on the less common vertical axis wind turbine (VAWT). The VAWT is a type of wind turbine where the main rotor shaft is set in a transverse position to the wind, turned across the shaft. Unlike the more traditional horizontal axis design, the works can be located at the base of the turbine, meaning more straightforward access to controls and maintenance of the machinery. Most importantly, VAWTs will work without being turned with the changing directions of wind, removing the need for wind-sensing and control systems.
The new VAWT design, funded to this stage by Green Future Investments through the Future Frontiers Fund, is J-shaped based: the span of the blades — essentially their height — is 3 metres with a spread of 2.5 metres in diameter. The new blade design works more effectively than others when it comes to low wind speeds, making sure there is no need for the kind of electricity supply and motors needed to move large turbines. The turbine has been through modelling analyses and found to work at wind speeds around 10 metres per second and below, as low as 3-5 metres per second. The J-shaped-based VAWT has a starting torque nearly 6% higher than obtained with a conventional aerofoil (the NACA0015, with similar aerodynamics to an aeroplane wing) under the same modelling conditions. This is an interesting result as it shows that the J-shaped-based VAWT can self-start more easily at low wind speed than the NACA0015-based VAWT. The specific maximum power output continues to be tested for and analysed via a 3D printed prototype, scaled down from the original model to 0.5 metre high.
An initial cost-analysis suggests that the newly designed wind turbine would cost around £82 for the materials of the tower, blades and struts, and will weigh around 117kg, a similar weight as existing turbines of this size. The total initial investment a resident has to make (the capital expenditure) which includes the purchase of batteries, tower, power inverter, etc, is approximately £7,300, which is below the average value for small-scale residential wind turbines available on the market (for the moment, though, the calculations do not yet include manufacturing costs and any labour costs for installation). The payback period is estimated to be around three years — compared with an average six to 10 years for solar panelling — making wind turbines a more practical proposition for businesses and householders.
In terms of society’s progress to a world of sustainable energy, and the increasing importance of more householders acting as ‘prosumers’ — producers as well as consumers — improved wind turbine designs are going to play a significant role. The energy output of each single VAWT may be relatively small, but they provide a realistic option for large numbers of homes as well as businesses and landowners for their estates: because of their size and cost, the ease of use and maintenance, and greater consistency of energy production throughout the seasons when compared with solar panelling. Systems that combine both VAWT and solar panelling have the potential to move homes towards energy self-sufficiency. While solar on its own continues to deliver only modest financial returns in the UK, the addition of a wind option will change the picture and encourage more people to become energy producers.
Larger property-owners, such as local authorities, airports, shopping centres and sites in urban areas, where the use of wind turbines has been impossible in the past, will increasingly be able to include energy production from extended batches of small wind turbines a key part of their sustainability strategies.
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